Heat pipe for vehicle energy-storage systems

ABSTRACT

Provided are cooling subsystems for a vehicle energy-storage system comprising a heat pipe disposed between two battery modules, the heat pipe being thermally coupled to each of a plurality of cells of the two battery modules at an end of each cell. The heat pipe comprises an envelope and a working fluid, the heat pipe transferring heat from the plurality of cells. Optionally, the cooling subsystem further includes a heat exchanger thermally coupled to the heat pipe, the heat exchanger receiving heat from the heat pipe.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.62/186,977 filed on Jun. 30, 2015. This application is related to U.S.patent application Ser. No. 14/841,617 filed on Aug. 31, 2015. Thesubject matter of the aforementioned applications is incorporated hereinby reference for all purposes.

FIELD

The present application relates generally to heat transfer, and morespecifically to heat transfer for vehicle energy-storage systems.

BACKGROUND

It should not be assumed that any of the approaches described in thissection qualify as prior art merely by virtue of their inclusion in thissection.

Electric-drive vehicles offer a solution for reducing the impact offossil-fuel engines on the environment and transforming automotivemobility into a sustainable mode of transportation. Energy-storagesystems are essential for electric-drive vehicles, such as hybridelectric vehicles, plug-in hybrid electric vehicles, and all-electricvehicles. However, present energy-storage systems have disadvantagesincluding large size, inefficiency, and poor safety, to name a few.Similar to many sophisticated electrical systems, heat in automotiveenergy-storage systems should be carefully managed. Current thermalmanagement schemes consume an inordinate amount of space. Presentenergy-storage systems also suffer from inefficiencies arising variouslyfrom imbalance among battery cells and resistance in various electricalconnections. In addition, current energy-storage systems are notadequately protected from forces such as crash forces encountered duringa collision.

SUMMARY

This summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used as an aid in determining the scope of the claimed subjectmatter.

According to various embodiments, the present disclosure may be directedto a cooling subsystem for a vehicle energy-storage system comprising: aheat pipe disposed between two battery modules, the heat pipe beingthermally coupled to each of a plurality of cells of the two batterymodules at an end of each cell, the heat pipe comprising an envelope anda working fluid, the heat pipe transferring heat from the plurality ofcells.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments are illustrated by way of example and not limitation in thefigures of the accompanying drawings, in which like references indicatesimilar elements.

FIG. 1 illustrates an example environment in which an energy-storagesystem can be used.

FIG. 2A shows an orientation of battery modules in an energy-storagesystem, according to various embodiments of the present disclosure.

FIG. 2B depicts a bottom part of an enclosure of a partial battery packsuch as shown in FIG. 2A.

FIG. 3 is a simplified diagram of a battery module, according to variousembodiments of the present disclosure.

FIG. 4 illustrates a half module, in accordance with variousembodiments.

FIGS. 5A and 5B show a current carrier, according to variousembodiments.

FIG. 6 depicts an example battery cell.

FIGS. 7A-7C illustrate further embodiments of a battery module.

DETAILED DESCRIPTION

While this disclosure is susceptible of embodiment in many differentforms, there are shown in the drawings and will herein be described indetail several specific embodiments with the understanding that thepresent disclosure is to be considered as an exemplification of theprinciples of the disclosure and is not intended to limit the disclosureto the embodiments illustrated. The terminology used herein is for thepurpose of describing particular embodiments only and is not intended tobe limiting of the disclosure. As used herein, the singular forms “a,”“an,” and “the” are intended to include the plural forms as well, unlessthe context clearly indicates otherwise. It will be further understoodthat the terms “comprises,” “comprising,” “includes,” and “including,”when used in this specification, specify the presence of statedfeatures, integers, steps, operations, elements, and/or components, butdo not preclude the presence or addition of one or more other features,integers, steps, operations, elements, components, and/or groupsthereof. It will be understood that like or analogous elements and/orcomponents, referred to herein, may be identified throughout thedrawings with like reference characters. It will be further understoodthat several of the figures are merely schematic representations of thepresent disclosure. As such, some of the components may have beendistorted from their actual scale for pictorial clarity.

Some embodiments of the present invention can be deployed in a wheeled,self-powered motor vehicle used for transportation, such as hybridelectric vehicles, plug-in hybrid electric vehicles, and all-electricvehicles. For example, FIG. 1 illustrates electric car 100. Electric car100 can be an automobile propelled by one or more electric motors 110.Electric motor 110 can be coupled to one or more wheels 120 through adrivetrain (not shown in FIG. 1). Electric car 100 can include frame 130(also known as an underbody or chassis). Frame 130 can be a supportingstructure of electric car 100 to which other components can beattached/mounted, such as, for example, a battery pack 140 a. Batterypack 140 a can supply electricity to power one or more electric motors110, for example, through an inverter. The inverter can change directcurrent (DC) from battery pack 140 a to alternating current (AC), as canbe required for electric motors 110, according to some embodiments.

As depicted in FIG. 1, battery pack 140 a may have a compact “footprint”and be at least partially enclosed by frame 130 and disposed to providea predefined separation, for example, from structural rails 150 of anupper body that couples to frame 130. Accordingly, at least one of arear crumple zone 160, front crumple zone 170, and lateral crumple zone180 can be formed around battery pack 140 a. Both the frame 130 andstructural rails 150 may protect battery pack 140 a from forces orimpacts exerted from outside of electric car 100, for example, in acollision. In contrast, other battery packs which extend past at leastone of structural rails 150, rear crumple zone 160, and front crumplezone 170 remain vulnerable to damage and may even explode in an impact.

Battery pack 140 a may have a compact “footprint” such that it may beflexibly used in and disposed on frame 130 having different dimensions.Battery pack 140 a can also be disposed in frame 130 to help improvedirectional stability (e.g., yaw acceleration). For example, batterypack 140 a can be disposed in frame 130 such that a center of gravity ofelectric car 100 is in front of the center of the wheelbase (e.g.,bounded by a plurality of wheels 120).

FIG. 2A shows battery pack 140 b with imaginary x-, y-, and z-axissuperimposed, according to various embodiments. Battery pack 140 b caninclude a plurality of battery modules 210. In a non-limiting example,battery pack 140 b can be approximately 1000 mm wide (along x-axis),1798 mm long (along y-axis), and 152 mm high (along z-axis), andincludes 36 of battery modules 210.

FIG. 2B illustrates exemplary enclosure 200 for battery pack 140 bhaving a cover removed for illustrative purposes. Enclosure 200 includesa tray 260 and a plurality of battery modules 210. Tray 260 may includepositive bus bar 220 and negative bus bar 230. Positive bus bar 220 canbe electrically coupled to a positive (+) portion of a power connectorof each battery module 210. Negative bus bar 230 can be electricallycoupled to a negative (−) portion of a power connector of each batterymodule 210. Positive bus bar 220 can be electrically coupled to positiveterminal 240 of enclosure 200. Negative bus bar 230 can be electricallycoupled to negative terminal 250 of enclosure 200. As described abovewith reference to FIG. 1, because bus bars 220 and 230 can be withinstructural rails 150, they can be protected from collision damage.

According to some embodiments, negative bus bar 230 and positive bus bar220 are disposed along opposite edges of tray 260 to provide apredefined separation between negative bus bar 230 and positive bus bar220. Such separation between negative bus bar 230 and positive bus bar220 can prevent or at least reduce the possibility of a short circuit(e.g., of battery pack 140 b) due to a deformity caused by an impact.

As will be described further in more detail with reference to FIG. 4,battery module 210 can include at least one battery cell (details notshown in FIG. 2A, see FIG. 7). The at least one battery cell can includean anode terminal, a cathode terminal, and a cylindrical body. Thebattery cell can be disposed in each of battery module 210 such that asurface of the anode terminal and a surface of the cathode terminal arenormal to the imaginary x-axis referenced in FIG. 2A (e.g., thecylindrical body of the battery cell is parallel to the imaginaryx-axis). This can be referred to as an x-axis cell orientation.

In the event of fire and/or explosion in one or more of battery modules210, the battery cells can be vented along the x-axis, advantageouslyminimizing a danger and/or a harm to a driver, passenger, cargo, and thelike, which may be disposed in electric car 100 above battery pack 140 b(e.g., along the z-axis), in various embodiments.

The x-axis cell orientation of battery modules 210 in battery pack 140 bshown in FIGS. 2A and 2B can be advantageous for efficient electricaland fluidic routing to each of battery module 210 in battery pack 140 b.For example, at least some of battery modules 210 can be electricallyconnected in a series (forming string 212), and two or more of string212 can be electrically connected in parallel. This way, in the eventone of string 212 fails, others of string 212 may not be affected,according to various embodiments.

FIG. 3 illustrates battery module 210 according to various embodiments.Main power connector 360 can provide power from battery cells 350 tooutside of battery module 210. In some embodiments, battery module 210includes two half modules 310 and 320 each having respective enclosure330. Enclosure 330 may be made using one or more plastics havingsufficiently low thermal conductivities. Respective enclosures 330 ofeach of two half modules 310 and 320 may be coupled with each other toform the housing for battery module 210.

FIG. 3 includes view 340 of enclosure 330 (e.g., with a cover removed).For each of half modules 310, 320 there is shown a plurality of batterycells 350 oriented (mounted) horizontally (see also FIG. 4). By way ofnon-limiting example, each half module includes 104 of battery cells350. By way of further non-limiting example, eight of battery cells 350are electrically connected in a series (e.g., the staggered column ofeight battery cells 350 shown in FIG. 3), with a total of thirteen ofsuch groups of eight battery cells 350 electrically connected in series.By way of additional non-limiting example, the thirteen groups (e.g.,staggered columns of eight battery cells 350 electrically coupled inseries) are electrically connected in parallel. This exampleconfiguration may be referred to as “8S13P” (8 series, 13 parallel).Other combinations and permutations of battery cells 350 electricallycoupled in series and/or parallel maybe used.

Additional thermal runaway control is provided in various embodiments byscoring on end 640 (identified in FIG. 6) of the battery cell 350. Thescoring promotes rupturing to effect venting in the event of excessivepressure.

FIG. 4 depicts a view of half module 310, 320 without enclosure 330 inaccordance with various embodiments. Half modules 310 and 320 need notbe the same, e.g., they may be mirror images of each other in someembodiments. Half modules 310 and 320 can include a plurality of batterycells 350. The plurality of battery cells 350 can be disposed betweencurrent carrier 410 and blast plate 420 such that an exterior side ofeach of battery cells 350 is not in contact with the exterior sides ofother (e.g., adjacent) battery cells 350. In this way, coolant cancirculate among and between battery cells 350 to provide submerged,evenly distributed cooling. In addition, to save the weight associatedwith coolant in areas where cooling is not needed, air pockets can beformed using channels craftily designed in space 430 between currentcarrier 410 and blast plate 420 not occupied by battery cells 350.

Coolant can enter half modules 310, 320 through coolant intake 440, beoptionally directed by one or more flow channels, circulate among andbetween the plurality of battery cells 350, and exits through coolantouttake 450. In some embodiments, coolant intake 440 and coolant outtake450 can each be male or female fluid fittings. In some embodiments,coolant or cooling fluid is at least one of: synthetic oil such aspoly-alpha-olefin (or poly-α-olefin, abbreviated as PAO) oil, ethyleneglycol and water, liquid dielectric cooling based on phase change, andthe like. Compared to techniques using metal tubes to circulate coolant,submerged cooling improves a packing density of battery cells 350 (e.g.,inside battery module 210 and half modules 310, 320) by 15%, in variousembodiments.

FIGS. 5A and 5B depict current carrier 410, 410A according to variousembodiments. Current carrier 410, 410A is generally flat (or planar) andcomprises one or more layers (not shown in FIGS. 5A and 5B), such as abase layer, a positive power plane, a negative power plane, and signalplane sandwiched in-between dielectric isolation layers (e.g., made ofpolyimide). In some embodiments, the signal plane can include signaltraces and be used to provide battery module telemetry (e.g., batterycell voltage, current, state of charge, and temperature from optionalsensors on current carrier 410) to outside of battery module 210.

As depicted in FIG. 5B, current carrier 410A can be a magnified view ofa portion of current carrier 410, for illustrative purposes. Currentcarrier 410A can be communicatively coupled to each of battery cells350, for example, at separate fused positive (+) portion 530 andseparate negative (−) portion 540 which may be electrically coupled tothe positive power plane and negative power plane (respectively) ofcurrent carrier 410A, and to each cathode and anode (respectively) ofbattery cell 350. In some embodiments, positive (+) portion 530 is laserwelded to a cathode terminal of battery cell 350, and negative (−)portion 540 is laser welded to an anode terminal of battery cell 350. Insome embodiments, the laser-welded connection has on the order of 5milli-Ohms resistance. In contrast, electrically coupling the elementsusing ultrasonic bonding of aluminum bond wires has on the order of 10milli-Ohms resistance. Laser welding advantageously has lower resistancefor greater power efficiency and can take less time to perform thanultrasonic wire bonding, which contribute to greater performance andmanufacturing efficiency.

Current carrier 410A can include fuse 550 formed from part of a metallayer (e.g., copper, aluminum, etc.) of current carrier 410A, such as inthe positive power plane. In some embodiments, fuse 550 is formed (e.g.,laser etched) in a metal layer (e.g., positive power plane) todimensions corresponding to a type of low-resistance resistor and actsas a sacrificial device to provide overcurrent protection. For example,in the event of thermal runaway of one of battery cell 350 (e.g., due toan internal short circuit), the fuse may “blow,” breaking the electricalconnection to battery cell 350 and electrically isolating battery cell350 from current carrier 410A. Although an example of a fuse formed inthe positive power plane was provided, a fuse may additionally oralternatively be a part of the negative power plane.

Additional thermal runaway control is provided in various embodiments byscoring on end 640 (identified in FIG. 6) of battery cell 350. Thescoring promoting rupturing to effect venting in the event of overpressure. In various embodiments, all battery cells 350 may be orientedto allow venting into blast plate 420 for both half modules 310, 320.

In some embodiments, current carrier 410 is comprised of a printedcircuit board and a flexible printed circuit. For example, the printedcircuit board may variously comprise at least one of copper, FR-2(phenolic cotton paper), FR-3 (cotton paper and epoxy), FR-4 (wovenglass and epoxy), FR-5 (woven glass and epoxy), FR-6 (matte glass andpolyester), G-10 (woven glass and epoxy), CEM-1 (cotton paper andepoxy), CEM-2 (cotton paper and epoxy), CEM-3 (non-woven glass andepoxy), CEM-4 (woven glass and epoxy), and CEM-5 (woven glass andpolyester). By way of further non-limiting example, the flexible printedcircuit may comprise at least one of copper foil and a flexible polymerfilm, such as polyester (PET), polyimide (PI), polyethylene naphthalate(PEN), polyetherimide (PEI), along with various fluoropolymers (FEP),and copolymers.

In addition to electrically coupling battery cells 350 to each other(e.g., in series and/or parallel), current carrier 410 provideselectrical connectivity to outside of battery module 210, for example,through main power connector 360 (FIG. 3). Current carrier 410 may alsoinclude electrical interface 460 (FIGS. 4, 5A) which transports signalsfrom the signal plane. Electrical interface 460 can include anelectrical connector (not shown in FIG. 4, 5A).

FIG. 6 shows battery cell 350 according to some embodiments. In someembodiments, battery cell 350 can be a lithium-ion (li-ion) battery. Forexample, battery cell 350 may be an 18650 type li-ion battery having acylindrical shape with an approximate diameter of 18.6 mm andapproximate length of 65.2 mm. Other rechargeable battery form factorsand chemistries can additionally or alternatively be used. In variousembodiments, battery cell 350 may include can 620 (e.g., the cylindricalbody), anode terminal 670, and cathode terminal 680. For example, anodeterminal 670 can be a negative terminal of battery cell 350 and cathodeterminal 680 can be a positive terminal of battery cell 350. Anodeterminal 670 and cathode terminal 680 can be electrically isolated fromeach other by an insulator or dielectric.

FIG. 7A illustrates an apparatus for heat transfer in battery module 210a, according to some embodiments. Battery module 210 a can comprise twohalf modules 310 and 320 and battery cells 350, as were described inrelation to FIG. 3. Half modules 310 and 320 may include a plurality ofbattery cells 350 which may be oriented (mounted) horizontally. In someembodiments, battery module 210 a does not include blast plate 420 (FIG.4).

According to some embodiments, battery module 210 a can include heatpipe 710 a. Heat pipe 710 a can comprise two side surfaces 720 which arethermally coupled to battery cells 350, for example, at end 640 (FIG.6). In various embodiments, side surfaces 720 can (also) be mechanicallycoupled to end 640 of battery cells 350, for example, using a thermaladhesive or glue (e.g., thermally conductive two-part epoxy resin). Insome embodiments, heat pipe 710 a can be thermally coupled andelectrically isolated from battery cells 350 using dielectric separationhaving (extremely) low electrical conductivity. For example, an exteriorsurface of heat pipe 710 a (including side surfaces 720) comprises atleast one of: aluminum oxide, diamond powder based materials, boronnitride, and the like. Heat pipe 710 a can transfer heat from batterycells 350.

An envelope (e.g., enclosure) of heat pipe 710 a may comprise at leastone thermally conductive material, such as aluminum, copper, steel,stainless steel, and a high-performance alloy (e.g., Hastelloy, Inconel,Waspaloy, Rene alloys, Haynes alloys, Incoloy, MP98T, TMS alloys, andCMSX single crystal alloys). The envelope of heat pipe 710 a can enclosea working fluid, such as ammonia, ethanol, methanol, water, refrigerant(e.g., R134a), nitrogen, oxygen, neon, hydrogen, helium, and alkalimetal (e.g., cesium, potassium, and sodium). The envelope and workingfluid pair may be selected for efficient heat transfer over an operatingtemperature range and for compatibility (e.g., to avoid problems such asnon-condensable gas generation, material transport, and corrosion). Insome embodiments, heat pipe 710 a includes a metallic envelope and aworking fluid, and has an operating temperature range of 20° C. to 150°C. The metallic envelope may be made of aluminum, copper, steel,stainless steel, or other high-performance alloys. The working fluid maybe a phase-charging coolant, such as ammonia, ethanol, methanol, water,refrigerant, nitrogen, oxygen, neon, hydrogen, helium, alkali metal, andthe like.

Heat pipe 710 a may be a sealed system roughly comprising evaporatorsection 730 and condenser section 740. For example, evaporator section730 contains the working fluid as both a saturated liquid and a vapor(gas phase). In operation, heat from battery cells 350 may be receivedby side surfaces 720 (e.g., evaporator section 730), vaporizing thesaturated liquid. The vapor can travel (up) to condenser section 740(e.g., via convection), where it is cooled and turned back to asaturated liquid. The condensed liquid can return to evaporator section730 (e.g., via gravity, capillary action, etc.).

FIG. 7B illustrates an apparatus for heat transfer in battery module 210b, according to some embodiments. Battery module 210 b can comprise twohalf modules 310 and 320 and battery cells 350, as were described inrelation to FIGS. 3 and 7A. Main power connector 360 (as described inrelation to FIG. 3) can be represented by male main power connector 360_(M), optional main power connector openings 360 _(P) (e.g., associatedwith half module 310, half module 320 (not depicted in FIG. 7B), andheat pipe 710 b) and female main power connector 360 _(F). In someembodiments, optional main power connector opening 360 _(P) (e.g., ofheat pipe 710 b) can be an electrical connector coupled to at least oneelectrical connector of half modules 310 and 320 (e.g., an associatedmain power connector opening 360 _(P)). In some embodiments, batterymodule 210 b does not include blast plate 420 (FIG. 4).

As shown in FIG. 7B, a condenser section of heat pipe 710 b is thermallyand/or physically coupled to optional heat exchanger 750. Heat exchanger750 may comprise at least one of aluminum, copper, an alloy of aluminumand copper, and the like. In operation, heat exchanger 750 may receiveheat from the condenser section of heat pipe 710 b and transfer the heatto another medium, such as coolant or cooling fluid. In someembodiments, heat exchanger 750 comprises aluminum. For example, thecoolant can enter heat exchanger 750 through one of ports 760 and 770(e.g., from a coolant system and/or sub-system) and can exit heatexchanger 750 (e.g., to the coolant system and/or sub-system) throughone of ports 770 and 760. An interior of heat exchanger 750 (not shownin FIG. 7B) may comprise a plurality of channels to circulate thecoolant inside heat exchanger 750 to efficiently transfer heat from thecondenser section of heat pipe 710 b to the coolant. For example, theplurality of channels can direct the coolant from one of ports 760 and770, circulate the coolant inside heat exchanger 750, and direct thecoolant to one of ports 770 and 760.

The coolant may be at least one of the following: synthetic oil, waterand ethylene glycol (WEG), poly-alpha-olefin (or poly-α-olefin, alsoabbreviated as PAO) oil, liquid dielectric cooling based on phasechange, and the like. In various embodiments, the coolant can be WEG. Byway of further non-limiting example, the coolant may be at least one of:perfluorohexane (Flutec PP1), perfluoromethylcyclohexane (Flutec PP2),Perfluoro-1,3-dimethylcyclohexane (Flutec PP3), perfluorodecalin (FlutecPP6), perfluoromethyldecalin (Flutec PP9), trichlorofluoromethane (Freon11), trichlorotrifluoroethane (Freon 113), methanol (methyl alcohol283-403K), ethanol (ethyl alcohol 273-403K), and the like.

In some embodiments, the coolant is provided (e.g., pumped) to batterypack 140 b (FIG. 2A) in tray 260 (FIG. 2B). Within battery pack 140 b,coolant may be circulated to each heat exchanger 750 in battery modules210 b. In this way, heat can be efficiently managed/dissipated andthermal gradient minimized among all battery cells in battery pack 140b, such that a temperature may be maintained at an approximately uniformlevel. Such a uniform temperature level can sustain a direct currentinternal resistance (DCIR) of each battery cell at a substantiallypredefined resistance. Since the DCIR can vary with a temperature,keeping each battery cell in battery pack 140 b at a substantiallyuniform and predefined temperature can result in each battery cellhaving substantially the same DCIR. Because a voltage across eachbattery cell can be reduced as a function of its respective DCIR, eachbattery cell in battery pack 140 b may experience substantially the sameloss in voltage. In this way, each battery cell in battery pack 140 bcan be maintained at approximately the same capacity and imbalancesbetween battery cells in battery pack 140 b can be minimized.

FIG. 7C shows some example constituent components—half module 310, heatpipe 710 b, optional heat exchanger 750, and half module 320—assembledinto battery module 210 a, according to various embodiments. In someembodiments, heat pipe 710 b has width 780 within a range of 2 mm-4 mmand heat exchanger 750 has width 485 within a range of 1 mm-10 mm. Invarious embodiments, heat pipe 710 b and heat exchanger 750 have length490 in a range of 250 mm-400 mm.

As would be readily appreciated by one of ordinary skill in the art,various embodiments described herein may be used in additionalapplications, such as in energy-storage systems for wind and solar powergeneration. Other applications are also possible.

The description of the present disclosure has been presented forpurposes of illustration and description, but is not intended to beexhaustive or limited to the invention in the form disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the invention.Exemplary embodiments were chosen and described in order to best explainthe principles of the present disclosure and its practical application,and to enable others of ordinary skill in the art to understand theinvention for various embodiments with various modifications as aresuited to the particular use contemplated.

What is claimed is:
 1. A cooling subsystem for a vehicle energy-storagesystem comprising: a heat pipe disposed between two battery modules, theheat pipe being thermally coupled to each of a plurality of cells of thetwo battery modules at an end of each cell, the heat pipe comprising anenvelope and a working fluid, the heat pipe transferring heat from theplurality of cells.
 2. The cooling subsystem of claim 1 furthercomprising: a heat exchanger thermally coupled to the heat pipe, theheat exchanger receiving heat from the heat pipe.
 3. The coolingsubsystem of claim 2, wherein the heat exchanger comprises at least oneof: aluminum, copper, and an aluminum-copper alloy.
 4. The coolingsubsystem of claim 3 further comprising: a coolant system forcirculating a coolant pumped into a battery tray such that a pluralityof battery modules disposed in the battery tray are at approximately thesame predetermined temperature, the heat exchanger being thermallycoupled to the coolant system using a coolant input port and a coolantoutput port.
 5. The cooling subsystem of claim 4, wherein the coolantcomprises at least one of: synthetic oil, water and ethylene glycol(WEG), poly-alpha-olefin oil, and liquid dielectric cooling based onphase change.
 6. The cooling subsystem of claim 1 wherein, the envelopecomprises at least one of: aluminum, copper, steel, stainless steel, anda high-performance alloy.
 7. The cooling subsystem of claim 6, whereinan exterior surface of the envelope comprises at least one of: aluminumoxide, diamond powder based materials, and boron nitride.
 8. The coolingsubsystem of claim 7, wherein the working fluid comprises at least oneof: ammonia, ethanol, methanol, water, refrigerant, nitrogen, oxygen,neon, hydrogen, helium, and alkali metal.
 9. The cooling subsystem ofclaim 1, wherein the envelope comprises aluminum, an exterior surface ofthe envelope comprises aluminum oxide, and the working fluid comprisesammonia.
 10. The cooling subsystem of claim 1, wherein the heat pipecomprises two sides that are substantially planar.
 11. A cooling systemfor a vehicle energy-storage system comprising: a heat pipe comprising aplanar surface thermally coupled to a plurality of cells of a batterymodule of the vehicle energy-storage system, the envelope beingconfigured to transfer heat from the plurality of cells; and a heatexchanger coupled to the envelope and configured to transfer the heatfrom the envelope, the heat exchanger comprising a channel configured todirect a working fluid through the heat exchanger to transfer the heatfrom the heat exchanger.
 12. The cooling system of claim 11, wherein theenvelope has a width of about 2 to 4 mm.
 13. The cooling system heatpipe of claim 12, wherein the heat exchanger comprises at least one of:aluminum, copper, and an aluminum-copper alloy.
 14. The cooling systemheat pipe of claim 13, wherein the heat exchanger is thermally coupledto a coolant system for circulating a coolant pumped into a battery traysuch that a plurality of battery modules disposed in the battery trayare at approximately the same predetermined temperature, the heatexchanger being thermally coupled to the coolant system through acoolant input port and a coolant output port.
 15. The cooling system ofclaim 14, wherein the coolant comprises at least one of: synthetic oil,water and ethylene glycol (WEG), poly-alpha-olefin oil, and liquiddielectric cooling based on phase change.
 16. The cooling system ofclaim 11 wherein, the envelope comprises at least one of: aluminum,copper, steel, stainless steel, and a high-performance alloy.
 17. Thecooling system of claim 16, wherein an exterior surface of the envelopecomprises at least one of: aluminum oxide, diamond powder basedmaterials, and boron nitride.
 18. The cooling system of claim 17,wherein the working fluid comprises at least one of: ammonia, ethanol,methanol, water, refrigerant, nitrogen, oxygen, neon, hydrogen, helium,and alkali metal.
 19. The cooling system of claim 11, wherein theenvelope comprises aluminum, an exterior surface of the envelopecomprises aluminum oxide, and the working fluid comprises ammonia. 20.The cooling system of claim 11, wherein the planar surface of the heatpipe is coupled to the plurality of cells through end sections of theplurality of cells.